Abstract: The new PX-2 thinning and filtrate reducer is a synthetic polymer, which is made from polyacrylonitrile hydrolyzed at high temperature and high pressure, and combined with modified agent at the temperature of 60~70℃, and then be activated by cation. The determination of molecular weight and adsorption power indicates that PX-2’s molecular weight reduced, but its adsorption power on Anqiu clay increased obviously. The evaluation of drilling fluid property indicates that PX-2 can reduce the viscosity, shear and fluid loss as well. It is much better than NH4-HPAN both in heat-resistance and shale control.